fair enough…it was though obviously an extreme damage scenario..whether any "overide" in whatever FADEC logic may have at least in the short term produced more thrust, or in extremis, on the contrary, may have added damage to the airplane, due to the motors completely disintegrating in a most uncontained way..hard to tell..?

the way I read the accident report, those motors were actually useless in terms of possible thrust generation after the bird strikes…that the engines still were turning somewhat may have helped with the hydraulics to control the airplane..guess at those low airspeeds, if the RAT is deployed at those low airspeeds it may also have difficulty in producing enough juice to power the flight controls..but they also instinctively were able to start the APU in addition..

but maybe someone with extensive A320 knowledge may be able to chime in on those scenarios..

whatever, Capt Sullenberger is one of my heroes….

If a piece of equipment is mechanically destroyed, you can't bring it back to life by changing the control from electronic to manual. Destroyed is destroyed.

Not true with turbines. There have been numerous examples of damaged engines producing reduced levels of thrust . . . ask me how I know.

Volcanic coating, internal and external FOD, icing, electronic fuel control and misfueling have all resulted in engines producing less than maximum thrust for some period of time.

As to bringing an item back to life(?) is an unanswerable question, but both GE & RR engines in Boeing aircraft have an ALT position for reduced capability electronic fuel control management. Non normal engine operation would specify selection of ALT mode which eliminates many built in protections and allows the engine operation.

Would this have helped . . . ? I don't know but it sure would have been nice to have the option. Maybe Airbuses have that option, but I haven't seen it mentioned.

Where did you "read" that?

That aircraft was equipped with CFM powerplants. It's the IAE engines that have the probe.

The FADEC never commanded idle thrust. (The pilots never commanded TOGA thrust either but that's another issue)

It was physical damage to the engines that robbed them of their ability to produce thrust.

Now, I don't know all the failure modes on the CFM because they don't train us that way anymore but the IAE has several failure modes. A few will cause an idle roll back but most result in uncommanded TOGA. On some of these failures control can be re-established through the auto-thrust system and on some you have two choices: TOGA or shuting down the engine.

The engines continued to produce hydraulic power throughout the accident sequence.

Electrical power will disconnect at sub-idle but the hydraulic pumps produce useful pressure until very, very late in the shutdown sequence.

The RAT will produce hydraulic power until very low airspeeds. It can have an electrical dropout at lower speeds depending upon the installed electrical system.

[/quote]But they will pull them both back to idle, as happened to Sully, correct? A distinction without a difference, still no thrust.[/quote]


The FADECS will not roll back thrust to idle. When auto thrust Airbus speak for auto throttles, is active and the aircraft is in a climb the Flight Management Computers will command full climb thrust and the FADECS will command full climb thrust. Only engine failure will result in less than full climb thrust.

In addition if at any time the pilot moves the thrust levers to TOGA full takeoff thrust is always commanded by the FADEC's

The IAE engines use EPR as the primary engine thrust indications for the FADEC however there is a back up N1 mode selectable by the pilot that will bypass a failed or damaged EPR system and allow full rated thrust.

The report was very clear the engines were incapable of thrust, and that this was NOT a control problem, but major structural damage to the rotating parts:

Disassembly and examination of the engines revealed that two LPC IGVs in each engine had fractured because of the bird ingestion and were subsequently ingested into the engine cores, where they initiated secondary damage to the LPC and HPC. Immediately thereafter, the engine cores were incapable of supplying power to the fans; therefore, the fans could no longer rotate and produce sufficient thrust to sustain flight.

The report did say this about FADECs:

The NTSB concludes that, if the accident engines’ electronic control system had been capable of informing the flight crewmembers about the continuing operational status of the engines, they would have been aware that thrust could not be restored and would not have spent valuable time trying to relight the engines, which were too damaged for any pilot action to make operational.

Mike C.

The report was very clear the engines were incapable of thrust, and that this was NOT a control problem, but major structural damage to the rotating parts:

Even the most basic jet, no FADEC, no fan etc, is not controlled by a throttle in the same way a piston engine is.

The thrust lever will connect to a metering unit which is closest in function to a propeller governor. This mechanical unit will control fuel flow (and bleed valve operation) in order to accelerate and decelerate the engine to match the thrust level commanded by Thrust Lever Angle.

When you advance the thrust lever in a straight jet you aren't directly controlling fuel flow to the combustion chamber. You are telling a mechanical governor or a governor/computer hybrid or a full FADEC system to accelerate the engine to maximum thrust. Fuel flow may then increase, decrease, increase and decrease again along with bleed valve movement, in order to smoothly accelerate the engine and then stabilize it at the commanded level of thrust without causing a flameout, compressor stall, overspeed or underspeed condition.

None of this works if the engine is significantly damaged and there is no way for a pilot to assume manual control of the fuel flow in any kind of jet engine.

There is no way to achieve what you propose.

Jon, I think I understand what you're getting at, and while you're right, I think you took what I said a bit too literally... I didn't intend to mean pilot → lever → direct control of fuel flow, but I shouldn't have said "override everything" if I didn't mean literally that; I should have said something different.

A rudimentary mechanical fuel control, based on a compressor speed governor (plus or minus a narrow range to allow for acceleration and deceleration), will work in an emergency... It will work OK even without a P3 input to trim it (or temperature inputs, or P1, or control of the bleeds, etc.), but in an emergency wouldn't you like an engine that was designed with this option? If you think that it's more trouble than it's worth then yes, I can see the merit is some arguments against it.

You mention accel and decel and that is a good point; an in-depth understanding of compressor aerodynamics is something pilots practically never have the occasion or need to learn. It is complicated (when you get into multiple bleeds, stators, and spools) and it takes a lot of development before an engine just works when you move the levers, never mind how difficult that is for designers to take into account how a FOD'ed engine might work.


I think you glossed over my most important point, that is how does the pilot know that the engine is significantly damaged beyond hope? From the gauges, from sound or feel? What are the gauges not telling you?

I wouldn't go so far as to say "any" kind of jet engine. The early engines on the 262 direct fuel control (their ease of operation and service lives were unsurprisingly poor). Some versions of the PT-6 have an emergency power lever that more or less directly meters fuel (maybe apples to oranges, it's a much simpler turboprop with a responsive spool up).

Anyway, most of this is academic. We're talking about a million-to-one scenario when both (or all) of the engines are badly damaged.



I hope that makes sense. We might be talking past each other or we might be agreeing without realizing it.